1. Field of the Invention
The present invention relates to a flexible tube for an endoscope used as an inserting part of an endoscope. The present invention also relates to a method of producing the flexible tube.
2. Description of the Related Art
Flexible tubes for an endoscope are generally formed in such a manner that a spiral coil having one or more superposed layers are covered with a reticulate tube, which in turn is covered with a flexible jacket. The flexible jacket is formed by either of covering a flexible tube material therewith or applying a molten thermoplastic synthetic resin material on the reticulate tube and curing the applied layer.
FIG. 6 shows a conventional flexible tube for the endoscope, which has a jacket 13 formed by first applying a molten thermoplastic synthetic resin material and then curing the applied layer. Obviously, a jacket material 1 has penetrated through openings in the reticulate tube 12 to bind the jacket 13 and the reticulate tube 12. A reference numeral 11 represents a spiral coil 11.
However, a combination between the spiral coil 11 and the reticulate tube 12 is so weak that as the result of repeat use of the endoscope, gaps form between the two members 11 and 12 and the flexible tube becomes increasingly soft to introduce difficulty in inserting the endoscope into a body cavity.
Another problem in the conventional flexible tube for the endoscope is shown in FIG. 7. When using the flexible tube, the flexible tube bends in various directions at small radii of curvature or reverts to a straight form. As a result, a silicone rubber tube covering a bundle of optical fibers 50 passing through the flexible tube is damaged by inner edges of the spiral coil 11, often causing the internal optical fibers to break and become deteriorated in optical performance.